The present invention relates to a control valve for construction equipment, and more particularly, a control valve for construction equipment having a holding valve to prevent the work device from descending due to its own weight when an actuator like the boom cylinder is in a neutral state
FIG. 1 is a sectional view of a control valve for construction equipment according to the conventional technology, and FIG. 2 is a hydraulic circuit diagram of the holding valve illustrated in FIG. 1.
Referring to FIGS. 1 and 2, the control valve for the construction equipment according to the conventional technology includes a valve body (2) having a spool that is installed between a hydraulic pump (P) and an actuator in order to drive the actuator (e.g. boom cylinder) using the hydraulic fluid of the hydraulic pump (P).
The valve body is configured with a pump passage (3) to which the hydraulic fluid is supplied from the hydraulic pump (P), a supply passage (4) communicating with the pump passage (3), and the actuator ports (5,6) connected to the actuator.
If the spool is shifted to the left or right direction by applying the pilot pressure (Pia or Pib), the hydraulic fluid of the hydraulic pump (P) is supplied to the actuator through one side of the actuator port (5), and the hydraulic fluid discharged from the actuator can be returned to a tank passage (7) through the other side of the actuator port (6).
In order to prevent the work device from descending when the spool (1) is in the neutral state, a holding poppet (8) is formed on the actuator port (5) so as to hold temporarily the load of the actuator.
The back pressure chamber of the holding poppet (8) is connected with a holding valve (10) having an auxiliary spool (9) which is shifted by the pilot pressure to release the holding load of the actuator.
A check valve (13) being able to open and close is installed on a drain path (12a) where the hydraulic fluid drained from a back pressure chamber (11) by the shift of the auxiliary spool (9) is transferred.
A piston (14) is installed on a back pressure chamber (15) of the auxiliary spool (9) and shifts the auxiliary spool when a pilot pressure (Pi1) is applied.
In order to shift the spool (1) to the left in the figure, a pilot pressure (Pib) is applied to the right pilot port of the valve body (2) while the pilot pressure (Pi1) is applied to the pilot port of the holding valve (10). Thus, the spool (1) is shifted to the left, and the auxiliary spool (9) is shifted downwards by the piston (14) activated by the pilot pressure (Pi1) (Refer to FIG. 1).
If the spool (1) is shifted to the left in the figure, the hydraulic fluid supplied to the pump passage (3) from the hydraulic pump (P) pushes a check valve (16) upwards, and is transferred to the supply passage (4). The hydraulic fluid transferred to the supply passage (4) is supplied to the actuator (e.g. boom cylinder) through the actuator port (6).
At this time, the hydraulic fluid discharged from the actuator is transferred to the actuator port (5), pushes up the holding poppet (8), passes through port (C1) to spool (1), and is drained to tank passage (7).
On the other hand, if the auxiliary spool (9) is shifted downwards in the figure, the hydraulic fluid of the holding poppet (8) passes through a path (17) that is opened by the shift of the auxiliary spool (9), and releases the checking function of the check valve (13) that is installed on the drain path (12a). Thus, the checking function of the holding poppet (8) can be released as the hydraulic fluid of the back pressure chamber (11) passes through the path (17) and the drain paths (12a, 12b), and is drained to the port (C1).
Also, if the spool (1) is shifted to the right in the figure by the pilot pressure (Pia) applied to the left pilot port, the hydraulic fluid supplied to the pump passage (3) from the hydraulic pump (P) pushes the check valve (16) upwards, is transferred to the supply passage (4), pushes up the holding poppet (8) on the actuator port, and then is supplied to the actuator through the actuator port (5). At this time, the hydraulic fluid discharged from the actuator passes through the actuator port (6) and the spool (1), and is drained to the tank passage (7).
If the spool (1) is to be shifted to the left in the figure, the pilot pressure (Pib) is applied to the right end of the spool (1) with the pilot pressure (Pi1) simultaneously applied to the piston (14).
If the pilot line and control valve (not shown in the figure) are added for newly generating the pilot pressure in order to shift another control valve other than the control valve in FIG. 1, the pilot line and control valve are installed in the outside of the valve body (2). Accordingly, the additional installation of the pilot line and control valve not only increases the manufacturing cost, but makes the space surrounding the valve body (2) confined, which causes inconvenience during the maintenance.
It is desirable to provide a control valve for construction equipment, in which a supply passage of pilot pressure and a control valve are formed within a holding valve, thereby saving the manufacturing cost as well as allowing better use of space.
In accordance with one aspect of an embodiment of the present invention, there is provided a control valve for construction equipment comprising; a valve body having a pump passage to which hydraulic fluid is supplied from a hydraulic pump, a supply passage that is configured to communicate with the pump passage, and actuator ports that is connected to an actuator; a spool that is installed within the valve body and shifted to enable the hydraulic fluid of the hydraulic pump to be supplied to the actuator through one of the actuator ports, and to return the hydraulic fluid discharged from the actuator to the tank passage through the other of the actuator ports; a holding valve that is provided with a holding poppet which is formed on one of the actuator ports and an auxiliary spool which is connected to a back pressure chamber of the holding poppet and shifted by a pilot pressure so as to release a holding load of the actuator; a control valve that is installed within the valve body (defined as a control valve to be shifted by the pilot pressure (Pi2); and a pilot pressure control valve that is shiftably installed within the holding valve and configured to apply or block the pilot pressure to the control valve through flow paths the pilot pressure, wherein the pilot pressure control valve is to be shifted by a pressure of hydraulic fluid drained from the back pressure chamber of the holding poppet when the auxiliary spool is shifted.
According to another aspect of the present invention, the actuator is the boom cylinder or the arm cylinder.
The pilot pressure control valve is formed of a poppet type pilot pressure control valve having a check function.
The pilot pressure control valve is also formed of a spool type pilot pressure control valve.
The flow paths comprise; a first flow path that is formed in the holding valve so that an inlet of the first flow path is communicating with a first pilot port to which the pilot pressure is applied so as to shift the auxiliary spool; a second flow path with its inlet connected to an outlet of the first flow path; and a third flow path in which an outlet of the third flow path is communicating with a second pilot port to which the pilot pressure is applied while an inlet of the third flow path is connected to an outlet of the second flow path, wherein the outlet of the third flow path is opened or closed by the shift of the pilot pressure control valve.
The holding valve includes a fourth flow path to which hydraulic fluid of a back pressure chamber of the pilot pressure control valve is drained when the pilot pressure control valve is shifted.
The holding valve includes a fifth flow path in which hydraulic fluid drained from the back pressure chamber of the holding poppet is supplied to a pressure receiving port of the pilot pressure control valve when the auxiliary spool is shifted.
The pilot pressure control valve includes a sixth flow path which selectively communicates the second pilot port with the back pressure chamber of the pilot pressure control valve in order to drain a pilot pressure of the second pilot port, if the pilot pressure applied to the control valve is blocked by the pilot pressure control valve shifted by a pressure of the hydraulic fluid pressure drained from the back pressure chamber of the holding poppet when the auxiliary spool is shifted.
According to other aspect of the present invention, the pilot pressure control valve shifted in an initial state opens an inlet through which the pilot pressure is applied to the control valve so as to shift the auxiliary spool, wherein the pilot pressure control valve shifted in an on-state where hydraulic fluid drained from the back pressure chamber of the holding poppet is applied to a pressure receiving port of the pilot pressure control valve by shifting the auxiliary spool blocks the inlet so that the pilot pressure is not applied to the control valve.
Further, the pilot pressure control valve shifted in an initial state blocks an inlet so that the pilot pressure is not applied to the control valve, wherein the pilot pressure control valve shifted in an on-state where hydraulic fluid drained from the back pressure chamber of the holding poppet is applied to a pressure receiving port of the pilot pressure control valve by shifting the auxiliary spool opens the inlet so that the pilot pressure is applied to the control valve.
According to the embodiment of the present invention having the above-described configuration, a supply path of pilot pressure and a pilot pressure control valve are installed within a holding valve in order to shift the control valve installed in the valve body, thereby saving the manufacturing cost as well as allowing better use of space.